Optical toys were very popular in the 19th century. Many were used as family entertainment. They were seen to be both educational and fun, and were given scientific names, often derived from Greek. Zoetrope translates as ‘Wheel of Life’, a name by which it is also known. It was invented by William Horner in 1834. It did not become popular until the later 19th century, when the American games manufacturer Milton Bradley patented it. Its principal is based on persistence of vision - the fact that the eye will remember an image for a brief moment. Pictures are printed on a strip of paper, which is placed inside the drum. This is then spun, and to anyone looking through the slits it appears that the image moves.